Imatinib (4-[(4-methyl-1-piperazinyl)methyl]-N-[4-methyl-3-[[4-(3-pyridyl)-2-pyrimidinyl]amino]phenyl]benzamide) is a tyrosine kinase (TK) inhibitor used for the treatment of chronic myeloid leukemia (CML) attributed to the Philadelphia chromosome (Ph+) (1). This chromosomal abnormality develops after a genetic translocation between chromosome 9 and chromosome 22, which leads to the expression of a constitutively activated Bcr-Abl TK that is no longer under normal regulation. This drug is also used for the treatment of gastrointestinal stromal tumors (GIST) that are caused by mutations in the closely related Kit or platelet-derived growth factor (PDGF) TKs (2). In addition, imatinib has been shown to be an effective treatment against a variety of other conditions that are characterized by the expression of Abl or c-Kit TKs (3). Although imatinib is a useful chemotherapeutic agent for the treatment of CML and GIST, patients undergoing therapy for these conditions often develop resistance to the drug as a result of secondary mutations in the TKs (4). Dasatinib is a dual inhibitor of Src/Abl and c-Kit that was recently approved for treatment of imatinib-refractory CML and Ph+ acute lymphoblastic leukemia (ALL) (5, 6). A [18F]fluorine derivative of dasatinib ([18F]-N-(2-chloro-6-methylphenyl)-2-(6-(4-(2-fluoroethyl)piperazin-1-yl)-2-methylpyrimidin-4-ylamino)thiazole-5-carboxamide ([18F]SKI-249380)) was synthesized to probe the role of Abl, Src, and c-Kit in tumor malignancies with positron emission tomography (PET) imaging in small animals (7).